Add filesize limits for document rendering engines and support partial/complete rendering

Summary:
Depends on D19238. Ref T13105. Give document engines some reasonable automatic support for degrading gracefully when someone tries to hexdump a 100MB file or similar.

Also, make "Video" sort above "Audio" for files which could be rendered either way.

Test Plan: Viewed audio, video, image, and other files. Adjusted limits and saw full, partial, and fallback/error rendering.

Maniphest Tasks: T13105

Differential Revision: https://secure.phabricator.com/D19239

webroot/rsrc/js/application/files/behavior-document-engine.js

@@ -27,6 +27,7 @@ JX.behavior('document-engine', function() {
       view = new JX.PHUIXActionView()
         .setName(spec.name)
         .setIcon(spec.icon)
+        .setIconColor(spec.color)
         .setHref(spec.engineURI);
 
       view.setHandler(JX.bind(null, function(spec, e) {